Saute mushrooms and onion in a medium non stick skillet until all liquid has evaporated. Sprinkle flour and salt over vegetables; toss to coat.
Whisk eggs and milk together in a large bowl. Sir in mushroom mixture and 1 1/2 cups (375 mL) cheese.
Pour egg mixture into the same skillet. Turn heat to low; cover and cook for 15 to 25 minutes, or until set.
Sprinkle parmesan, remaining swiss cheese and bacon over frittata. If skillet is ovenproof, place under broiler until cheese melts, or cover skillet until cheese melts